Systems and methods for limiting voltage in wireless power receivers

ABSTRACT

This disclosure provides systems, methods, and apparatus for the limiting of voltage in wireless power receivers. In one aspect, an apparatus includes a power transfer component configured to receive power wirelessly from a transmitter. The apparatus further includes a circuit coupled to the power transfer component and configured to reduce a received voltage when activated. The apparatus further includes a controller configured to activate the circuit when the received voltage reaches a first threshold value and configured to deactivate the circuit when the received voltage reaches a second threshold value. The apparatus further includes an antenna configured to generate a signal to the transmitter that signals to the transmitter that the received voltage reached the first threshold value.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/622,204, filed Sep. 18, 2012, which claims priority under 35 U.S.C.§119(e) to U.S. Provisional Patent Application No. 61/591,201, entitled“SYSTEMS AND METHODS FOR LIMITING VOLTAGE IN WIRELESS POWER RECEIVERS,”filed on Jan. 26, 2012; and to U.S. Provisional Patent Application No.61/550,173, entitled “INTEGRATED SIGNALING AND PROTECTION FOR WIRELESSPOWER SYSTEM,” filed on Oct. 21, 2011; the entire contents of each ofwhich is herewith incorporated by reference.

FIELD

The present invention relates generally to wireless power. Morespecifically, the disclosure is directed to limiting voltage in wirelesspower receivers.

BACKGROUND

An increasing number and variety of electronic devices are powered viarechargeable batteries. Such devices include mobile phones, portablemusic players, laptop computers, tablet computers, computer peripheraldevices, communication devices (e.g., Bluetooth devices), digitalcameras, hearing aids, and the like. While battery technology hasimproved, battery-powered electronic devices increasingly require andconsume greater amounts of power. As such, these devices constantlyrequire recharging. Rechargeable devices are often charged via wiredconnections through cables or other similar connectors that arephysically connected to a power supply. Cables and similar connectorsmay sometimes be inconvenient or cumbersome and have other drawbacks.Wireless charging systems that are capable of transferring power in freespace to be used to charge rechargeable electronic devices or providepower to electronic devices may overcome some of the deficiencies ofwired charging solutions. As such, wireless power transfer systems andmethods that efficiently and safely transfer power to electronic devicesare desirable.

SUMMARY OF THE INVENTION

Various implementations of systems, methods and devices within the scopeof the appended claims each have several aspects, no single one of whichis solely responsible for the desirable attributes described herein.Without limiting the scope of the appended claims, some prominentfeatures are described herein.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims. Note thatthe relative dimensions of the following figures may not be drawn toscale.

One aspect of the disclosure provides an apparatus to receive powerwirelessly from a transmitter. The apparatus comprises a power transfercomponent configured to receive power wirelessly from the transmitter.The apparatus further comprises a circuit coupled to the power transfercomponent, the circuit configured to reduce a received voltage whenactivated. The apparatus further comprises a controller configured toactivate the circuit when the received voltage reaches a first thresholdvalue and configured to deactivate the circuit when the received voltagereaches a second threshold value. The apparatus further comprises anantenna configured to generate a signal received by the transmitter thatsignals to the transmitter that the received voltage reached the firstthreshold value.

Another aspect of the disclosure provides a method for limiting voltagein a wireless power receiver. The method comprises receiving powerwirelessly from a transmitter. The method further comprises measuring avalue of a received voltage. The method further comprises activating acircuit when the received voltage reaches a first threshold value, thecircuit configured to reduce the received voltage. The method furthercomprises generating a pulse received by the transmitter when thecircuit is activated that signals to the transmitter that the receivedvoltage reached the first threshold value. The method further comprisesdeactivating the circuit when the received voltage reaches a secondthreshold value.

Another aspect of the disclosure provides an apparatus configured tolimit voltage in a wireless power receiver. The apparatus comprisesmeans for receiving power wirelessly from a transmitter. The apparatusfurther comprises means for measuring a value of a received voltage. Theapparatus further comprises means for activating a circuit when thereceived voltage reaches a first threshold value, the circuit configuredto reduce the received voltage. The apparatus further comprises meansfor generating a pulse received by the transmitter when the circuit isactivated that signals to the transmitter that the received voltagereached the first threshold value. The apparatus further comprises meansfor deactivating the circuit when the received voltage reaches a secondthreshold value.

Another aspect of the disclosure provides a non-transitorycomputer-readable medium comprising code that, when executed, causes anapparatus to receive power wirelessly from a transmitter. The mediumfurther comprises code that, when executed, causes the apparatus tomeasure a value of a received voltage. The medium further comprises codethat, when executed, causes the apparatus to activate a circuit when thereceived voltage reaches a first threshold value, the circuit configuredto reduce the received voltage. The medium further comprises code that,when executed, causes the apparatus to generate a pulse received by thetransmitter when the circuit is activated that signals to thetransmitter that the received voltage reached the first threshold value.The medium further comprises code that, when executed, causes theapparatus to deactivate the circuit when the received voltage reaches asecond threshold value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of an exemplary wireless powertransfer system, in accordance with exemplary embodiments of theinvention.

FIG. 2 is a functional block diagram of exemplary components that may beused in the wireless power transfer system of FIG. 1, in accordance withvarious exemplary embodiments of the invention.

FIG. 3 is a schematic diagram of a portion of transmit circuitry orreceive circuitry of FIG. 2 including a transmit or receive coil, inaccordance with exemplary embodiments of the invention.

FIG. 4 is a functional block diagram of a transmitter that may be usedin the wireless power transfer system of FIG. 1, in accordance withexemplary embodiments of the invention.

FIG. 5 is a functional block diagram of a receiver that may be used inthe wireless power transfer system of FIG. 1, in accordance withexemplary embodiments of the invention.

FIG. 6 is a schematic diagram of a portion of transmit circuitry thatmay be used in the transmit circuitry of FIG. 4.

FIG. 7 is a functional block diagram of a receiver that may be used inthe wireless power transfer system of FIG. 1, in accordance withexemplary embodiments of the invention.

FIG. 8A is a schematic diagram of a receiver with a portion of a receivecoil and a switching and signaling circuitry that may be used in thereceiver of FIG. 7.

FIG. 8B is a schematic diagram of a portion of a transmitter that may beused in the transmit circuitry of FIG. 6.

FIG. 9 is a timing diagram of signals that may be generated by areceiver that may be used in the wireless power transfer system of FIG.1, in accordance with exemplary embodiments of the invention.

FIG. 10 is another timing diagram of signals that may be generated by areceiver that may be used in the wireless power transfer system of FIG.1, in accordance with exemplary embodiments of the invention.

FIG. 11 is another timing diagram of signals that may be generated by areceiver that may be used in the wireless power transfer system of FIG.1, in accordance with exemplary embodiments of the invention.

FIG. 12A is a partial state diagram of an overvoltage protection schemefor a receiver that may be used in the receiver of FIG. 8A.

FIG. 12B is another partial state diagram of an overvoltage protectionscheme for a receiver that may be used in the receiver of FIG. 8A.

FIG. 13 is a state diagram of a transmitter that may be used in thewireless power transfer system of FIG. 1, in accordance with exemplaryembodiments of the invention.

FIG. 14 is a state diagram of a receiver that may be used in thereceiver of FIG. 8A.

FIG. 15 is a diagram of exemplary receiver control threshold values thatmay be used in the receiver of FIG. 8A.

FIG. 16 is a screenshot of a simulation result in accordance withexemplary embodiments of the invention.

FIG. 17 is another screenshot of a simulation result in accordance withexemplary embodiments of the invention.

FIG. 18 is a flowchart of an exemplary method for limiting voltage in awireless power receiver.

FIG. 19 is a functional block diagram of a receiver, in accordance withan exemplary embodiment of the invention.

The various features illustrated in the drawings may not be drawn toscale. Accordingly, the dimensions of the various features may bearbitrarily expanded or reduced for clarity. In addition, some of thedrawings may not depict all of the components of a given system, methodor device. Finally, like reference numerals may be used to denote likefeatures throughout the specification and figures.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of exemplary embodiments of theinvention and is not intended to represent the only embodiments in whichthe invention may be practiced. The term “exemplary” used throughoutthis description means “serving as an example, instance, orillustration,” and should not necessarily be construed as preferred oradvantageous over other exemplary embodiments. The detailed descriptionincludes specific details for the purpose of providing a thoroughunderstanding of the exemplary embodiments of the invention. Theexemplary embodiments of the invention may be practiced without thesespecific details. In some instances, well-known structures and devicesare shown in block diagram form in order to avoid obscuring the noveltyof the exemplary embodiments presented herein.

Wirelessly transferring power may refer to transferring any form ofenergy associated with electric fields, magnetic fields, electromagneticfields, or otherwise from a transmitter to a receiver without the use ofphysical electrical conductors (e.g., power may be transferred throughfree space). The power output into a wireless field (e.g., a magneticfield) may be received, captured by, or coupled by a “receiving coil” toachieve power transfer.

FIG. 1 is a functional block diagram of an exemplary wireless powertransfer system 100, in accordance with exemplary embodiments of theinvention. Input power 102 may be provided to a transmitter 104 from apower source (not shown) for generating a field 105 for providing energytransfer. A receiver 108 may couple to the field 105 and generate outputpower 110 for storing or consumption by a device (not shown) coupled tothe output power 110. Both the transmitter 104 and the receiver 108 areseparated by a distance 112. In one exemplary embodiment, transmitter104 and receiver 108 are configured according to a mutual resonantrelationship. When the resonant frequency of receiver 108 and theresonant frequency of transmitter 104 are substantially the same or veryclose, transmission losses between the transmitter 104 and the receiver108 are minimal. As such, wireless power transfer may be provided overlarger distance in contrast to purely inductive solutions that mayrequire large coils that require coils to be very close (e.g., mms).Resonant inductive coupling techniques may thus allow for improvedefficiency and power transfer over various distances and with a varietyof inductive coil configurations.

The receiver 108 may receive power when the receiver 108 is located inan energy field 105 produced by the transmitter 104. The field 105corresponds to a region where energy output by the transmitter 104 maybe captured by a receiver 105. In some cases, the field 105 maycorrespond to the “near-field” of the transmitter 104 as will be furtherdescribed below. The transmitter 104 may include a transmit coil 114 foroutputting an energy transmission. The receiver 108 further includes areceive coil 118 for receiving or capturing energy from the energytransmission. The near-field may correspond to a region in which thereare strong reactive fields resulting from the currents and charges inthe transmit coil 114 that minimally radiate power away from thetransmit coil 114. In some cases the near-field may correspond to aregion that is within about one wavelength (or a fraction thereof) ofthe transmit coil 114. The transmit and receive coils 114 and 118 aresized according to applications and devices to be associated therewith.As described above, efficient energy transfer may occur by coupling alarge portion of the energy in a field 105 of the transmit coil 114 to areceive coil 118 rather than propagating most of the energy in anelectromagnetic wave to the far field. When positioned within the field105, a “coupling mode” may be developed between the transmit coil 114and the receive coil 118. The area around the transmit and receive coils114 and 118 where this coupling may occur is referred to herein as acoupling-mode region.

FIG. 2 is a functional block diagram of exemplary components that may beused in the wireless power transfer system 100 of FIG. 1, in accordancewith various exemplary embodiments of the invention. The transmitter 204may include transmit circuitry 206 that may include an oscillator 222, adriver circuit 224, and a filter and matching circuit 226. Theoscillator 222 may be configured to generate a signal at a desiredfrequency, such as 468.75 KHz, 6.78 MHz or 13.56 MHz, that may beadjusted in response to a frequency control signal 223. The oscillatorsignal may be provided to a driver circuit 224 configured to drive thetransmit coil 214 at, for example, a resonant frequency of the transmitcoil 214. The driver circuit 224 may be a switching amplifier configuredto receive a square wave from the oscillator 222 and output a sine wave.For example, the driver circuit 224 may be a class E amplifier. A filterand matching circuit 226 may be also included to filter out harmonics orother unwanted frequencies and match the impedance of the transmitter204 to the transmit coil 214.

The receiver 208 may include receive circuitry 210 that may include amatching circuit 232 and a rectifier and switching circuit 234 togenerate a DC power output from an AC power input to charge a battery236 as shown in FIG. 2 or to power a device (not shown) coupled to thereceiver 108. The matching circuit 232 may be included to match theimpedance of the receive circuitry 210 to the receive coil 218. Thereceiver 208 and transmitter 204 may additionally communicate on aseparate communication channel 219 (e.g., Bluetooth, zigbee, cellular,etc). The receiver 208 and transmitter 204 may alternatively communicatevia in-band signaling using characteristics of the wireless field 206.

As described more fully below, receiver 208, that may initially have aselectively disablable associated load (e.g., battery 236), may beconfigured to determine whether an amount of power transmitted bytransmitter 204 and receiver by receiver 208 is appropriate for charginga battery 236. Further, receiver 208 may be configured to enable a load(e.g., battery 236) upon determining that the amount of power isappropriate. In some embodiments, a receiver 208 may be configured todirectly utilize power received from a wireless power transfer fieldwithout charging of a battery 236. For example, a communication device,such as a near-field communication (NFC) or radio-frequencyidentification device (RFID may be configured to receive power from awireless power transfer field and communicate by interacting with thewireless power transfer field and/or utilize the received power tocommunicate with a transmitter 204 or other devices.

FIG. 3 is a schematic diagram of a portion of transmit circuitry 206 orreceive circuitry 210 of FIG. 2 including a transmit or receive coil352, in accordance with exemplary embodiments of the invention. Asillustrated in FIG. 3, transmit or receive circuitry 350 used inexemplary embodiments may include a coil 352. The coil may also bereferred to or be configured as a “loop” antenna 352. The coil 352 mayalso be referred to herein or be configured as a “magnetic” antenna oran induction coil. The term “coil” is intended to refer to a componentthat may wirelessly output or receive energy for coupling to another“coil.” The coil may also be referred to as an “antenna” of a type thatis configured to wirelessly output or receive power. The coil 352 may beconfigured to include an air core or a physical core such as a ferritecore (not shown). Air core loop coils may be more tolerable toextraneous physical devices placed in the vicinity of the core.Furthermore, an air core loop coil 352 allows the placement of othercomponents within the core area. In addition, an air core loop may morereadily enable placement of the receive coil 218 (FIG. 2) within a planeof the transmit coil 214 (FIG. 2) where the coupled-mode region of thetransmit coil 214 (FIG. 2) may be more powerful.

As stated, efficient transfer of energy between the transmitter 104 andreceiver 108 may occur during matched or nearly matched resonancebetween the transmitter 104 and the receiver 108. However, even whenresonance between the transmitter 104 and receiver 108 are not matched,energy may be transferred, although the efficiency may be affected.Transfer of energy occurs by coupling energy from the field 105 of thetransmitting coil to the receiving coil residing in the neighborhoodwhere this field 105 is established rather than propagating the energyfrom the transmitting coil into free space.

The resonant frequency of the loop or magnetic coils is based on theinductance and capacitance. Inductance may be simply the inductancecreated by the coil 352, whereas, capacitance may be added to the coil'sinductance to create a resonant structure at a desired resonantfrequency. As a non-limiting example, capacitor 352 and capacitor 354may be added to the transmit or receive circuitry 350 to create aresonant circuit that selects a signal 356 at a resonant frequency.Accordingly, for larger diameter coils, the size of capacitance neededto sustain resonance may decrease as the diameter or inductance of theloop increases. Furthermore, as the diameter of the coil increases, theefficient energy transfer area of the near-field may increase. Otherresonant circuits formed using other components are also possible. Asanother non-limiting example, a capacitor may be placed in parallelbetween the two terminals of the coil 352. For transmit coils, a signal358 with a frequency that substantially corresponds to the resonantfrequency of the coil 352 may be an input to the coil 352.

In one embodiment, the transmitter 104 may be configured to output atime varying magnetic field with a frequency corresponding to theresonant frequency of the transmit coil 114. When the receiver is withinthe field 105, the time varying magnetic field may induce a current inthe receive coil 118. As described above, if the receive coil 118 isconfigured to be resonant at the frequency of the transmit coil 118,energy may be efficiently transferred. The AC signal induced in thereceive coil 118 may be rectified as described above to produce a DCsignal that may be provided to charge or to power a load.

FIG. 4 is a functional block diagram of a transmitter 404 that may beused in the wireless power transfer system of FIG. 1, in accordance withexemplary embodiments of the invention. The transmitter 404 may includetransmit circuitry 406 and a transmit coil 414. The transmit coil 414may be the coil 352 as shown in FIG. 3. Transmit circuitry 406 mayprovide RF power to the transmit coil 414 by providing an oscillatingsignal resulting in generation of energy (e.g., magnetic flux) about thetransmit coil 414. Transmitter 404 may operate at any suitablefrequency.

Transmit circuitry 406 may include a fixed impedance matching circuit409 for matching the impedance of the transmit circuitry 406 (e.g., 50ohms) to the transmit coil 414 and a low pass filter (LPF) 408configured to reduce harmonic emissions to levels to preventself-jamming of devices coupled to receivers 108 (FIG. 1). Otherexemplary embodiments may include different filter topologies, includingbut not limited to, notch filters that attenuate specific frequencieswhile passing others and may include an adaptive impedance match, thatmay be varied based on measurable transmit metrics, such as output powerto the coil 414 or DC current drawn by the driver circuit 424. Transmitcircuitry 406 further includes a driver circuit 424 configured to drivean RF signal as determined by an oscillator 423. The transmit circuitry406 may be comprised of discrete devices or circuits, or alternately,may be comprised of an integrated assembly. An exemplary RF power outputfrom transmit coil 414 may be on the order of 2.5 Watts.

Transmit circuitry 406 may further include a controller 415 forselectively enabling the oscillator 423 during transmit phases (or dutycycles) for specific receivers, for adjusting the frequency or phase ofthe oscillator 423, and for adjusting the output power level forimplementing a communication protocol for interacting with neighboringdevices through their attached receivers. It is noted that thecontroller 415 may also be referred to herein as processor 415.Adjustment of oscillator phase and related circuitry in the transmissionpath may allow for reduction of out of band emissions, especially whentransitioning from one frequency to another.

The transmit circuitry 406 may further include a load sensing circuit416 for detecting the presence or absence of active receivers in thevicinity of the near-field generated by transmit coil 414. By way ofexample, a load sensing circuit 416 monitors the current flowing to thedriver circuit 424, that may be affected by the presence or absence ofactive receivers in the vicinity of the field generated by transmit coil414 as will be further described below. Detection of changes to theloading on the driver circuit 424 are monitored by controller 415 foruse in determining whether to enable the oscillator 423 for transmittingenergy and to communicate with an active receiver. As described morefully below, a current measured at the driver circuit 424 may be used todetermine whether an invalid device is positioned within a wirelesspower transfer region of the transmitter 404.

The transmit coil 414 may be implemented with a Litz wire or as anantenna strip with the thickness, width and metal type selected to keepresistive losses low. In a one implementation, the transmit coil 414 maygenerally be configured for association with a larger structure such asa table, mat, lamp or other less portable configuration. Accordingly,the transmit coil 414 generally may not need “turns” in order to be of apractical dimension. An exemplary implementation of a transmit coil 414may be “electrically small” (i.e., fraction of the wavelength) and tunedto resonate at lower usable frequencies by using capacitors to definethe resonant frequency.

The transmitter 404 may gather and track information about thewhereabouts and status of receiver devices that may be associated withthe transmitter 404. Thus, the transmit circuitry 406 may include apresence detector 480, an enclosed detector 460, or a combinationthereof, connected to the controller 415 (also referred to as aprocessor herein). The controller 415 may adjust an amount of powerdelivered by the driver circuit 424 in response to presence signals fromthe presence detector 480 and the enclosed detector 460. The transmitter404 may receive power through a number of power sources, such as, forexample, an AC-DC converter (not shown) to convert conventional AC powerpresent in a building, a DC-DC converter (not shown) to convert aconventional DC power source to a voltage suitable for the transmitter404, or directly from a conventional DC power source (not shown).

As a non-limiting example, the presence detector 480 may be a motiondetector utilized to sense the initial presence of a device to becharged that is inserted into the coverage area of the transmitter 404.After detection, the transmitter 404 may be turned on and the RF powerreceived by the device may be used to toggle a switch on the Rx devicein a pre-determined manner, which in turn results in changes to thedriving point impedance of the transmitter 404.

As another non-limiting example, the presence detector 480 may be adetector capable of detecting a human, for example, by infrareddetection, motion detection, or other suitable means. In some exemplaryembodiments, there may be regulations limiting the amount of power thata transmit coil 414 may transmit at a specific frequency. In some cases,these regulations are meant to protect humans from electromagneticradiation. However, there may be environments where a transmit coil 414is placed in areas not occupied by humans, or occupied infrequently byhumans, such as, for example, garages, factory floors, shops, and thelike. If these environments are free from humans, it may be permissibleto increase the power output of the transmit coil 414 above the normalpower restrictions regulations. In other words, the controller 415 mayadjust the power output of the transmit coil 414 to a regulatory levelor lower in response to human presence and adjust the power output ofthe transmit coil 414 to a level above the regulatory level when a humanis outside a regulatory distance from the electromagnetic field of thetransmit coil 414.

As a non-limiting example, the enclosed detector 460 (may also bereferred to herein as an enclosed compartment detector or an enclosedspace detector) may be a device such as a sense switch for determiningwhen an enclosure is in a closed or open state. When a transmitter is inan enclosure that is in an enclosed state, a power level of thetransmitter may be increased.

In exemplary embodiments, a method by which the transmitter 404 does notremain on indefinitely may be used. In this case, the transmitter 404may be programmed to shut off after a user-determined amount of time.This feature prevents the transmitter 404, notably the driver circuit424, from running long after the wireless devices in its perimeter arefully charged. This event may be due to the failure of the circuit todetect the signal sent from either the repeater or the receive coil thata device is fully charged. To prevent the transmitter 404 fromautomatically shutting down if another device is placed in itsperimeter, the transmitter 404 automatic shut off feature may beactivated only after a set period of lack of motion detected in itsperimeter. The user may be able to determine the inactivity timeinterval, and change it as desired. As a non-limiting example, the timeinterval may be longer than that needed to fully charge a specific typeof wireless device under the assumption of the device being initiallyfully discharged.

FIG. 5 is a functional block diagram of a receiver 508 that may be usedin the wireless power transfer system of FIG. 1, in accordance withexemplary embodiments of the invention. The receiver 508 includesreceive circuitry 510 that may include a receive coil 518. Receiver 508further couples to device 550 for providing received power thereto. Itshould be noted that receiver 508 is illustrated as being external todevice 550 but may be integrated into device 550. Energy may bepropagated wirelessly to receive coil 518 and then coupled through therest of the receive circuitry 510 to device 550. By way of example, thecharging device may include devices such as mobile phones, portablemusic players, laptop computers, tablet computers, computer peripheraldevices, communication devices (e.g., Bluetooth devices), digitalcameras, hearing aids (an other medical devices), and the like.

Receive coil 518 may be tuned to resonate at the same frequency, orwithin a specified range of frequencies, as transmit coil 414 (FIG. 4).Receive coil 518 may be similarly dimensioned with transmit coil 414 ormay be differently sized based upon the dimensions of the associateddevice 550. By way of example, device 550 may be a portable electronicdevice having diametric or length dimension smaller that the diameter oflength of transmit coil 414. In such an example, receive coil 518 may beimplemented as a multi-turn coil in order to reduce the capacitancevalue of a tuning capacitor (not shown) and increase the receive coil'simpedance. By way of example, receive coil 518 may be placed around thesubstantial circumference of device 550 in order to maximize the coildiameter and reduce the number of loop turns (i.e., windings) of thereceive coil 518 and the inter-winding capacitance.

Receive circuitry 510 may provide an impedance match to the receive coil518. Receive circuitry 510 includes power conversion circuitry 506 forconverting a received RF energy source into charging power for use bythe device 550. Power conversion circuitry 506 includes an RF-to-DCconverter 520 and may also in include a DC-to-DC converter 522. RF-to-DCconverter 520 rectifies the RF energy signal received at receive coil518 into a non-alternating power with an output voltage represented byV_(reg). The DC-to-DC converter 522 (or other power regulator) convertsthe rectified RF energy signal into an energy potential (e.g., voltage)that is compatible with device 550 with an output voltage and outputcurrent represented by V_(out) and I_(out). Various RF-to-DC convertersare contemplated, including partial and full rectifiers, regulators,bridges, doublers, as well as linear and switching converters.

Receive circuitry 510 may further include switching circuitry 512 forconnecting receive coil 518 to the power conversion circuitry 506 oralternatively for disconnecting the power conversion circuitry 506.Disconnecting receive coil 518 from power conversion circuitry 506 notonly suspends charging of device 550, but also changes the “load” as“seen” by the transmitter 404 (FIG. 2).

As disclosed above, transmitter 404 includes load sensing circuit 416that may detect fluctuations in the bias current provided to transmitterdriver circuit 424. Accordingly, transmitter 404 has a mechanism fordetermining when receivers are present in the transmitter's near-field.

When multiple receivers 508 are present in a transmitter's near-field,it may be desirable to time-multiplex the loading and unloading of oneor more receivers to enable other receivers to more efficiently coupleto the transmitter. A receiver 508 may also be cloaked in order toeliminate coupling to other nearby receivers or to reduce loading onnearby transmitters. This “unloading” of a receiver is also known hereinas a “cloaking.” Furthermore, this switching between unloading andloading controlled by receiver 508 and detected by transmitter 404 mayprovide a communication mechanism from receiver 508 to transmitter 404as is explained more fully below. Additionally, a protocol may beassociated with the switching that enables the sending of a message fromreceiver 508 to transmitter 404. By way of example, a switching speedmay be on the order of 100 μsec.

In an exemplary embodiment, communication between the transmitter 404and the receiver 508 refers to a device sensing and charging controlmechanism, rather than conventional two-way communication (i.e., in bandsignaling using the coupling field). In other words, the transmitter 404may use on/off keying of the transmitted signal to adjust whether energyis available in the near-field. The receiver may interpret these changesin energy as a message from the transmitter 404. From the receiver side,the receiver 508 may use tuning and de-tuning of the receive coil 518 toadjust how much power is being accepted from the field. In some cases,the tuning and de-tuning may be accomplished via the switching circuitry512. The transmitter 404 may detect this difference in power used fromthe field and interpret these changes as a message from the receiver508. It is noted that other forms of modulation of the transmit powerand the load behavior may be utilized.

Receive circuitry 510 may further include signaling detector and beaconcircuitry 514 used to identify received energy fluctuations, that maycorrespond to informational signaling from the transmitter to thereceiver. Furthermore, signaling and beacon circuitry 514 may also beused to detect the transmission of a reduced RF signal energy (i.e., abeacon signal) and to rectify the reduced RF signal energy into anominal power for awakening either un-powered or power-depleted circuitswithin receive circuitry 510 in order to configure receive circuitry 510for wireless charging.

Receive circuitry 510 further includes processor 516 for coordinatingthe processes of receiver 508 described herein including the control ofswitching circuitry 512 described herein. Cloaking of receiver 508 mayalso occur upon the occurrence of other events including detection of anexternal wired charging source (e.g., wall/USB power) providing chargingpower to device 550. Processor 516, in addition to controlling thecloaking of the receiver, may also monitor beacon circuitry 514 todetermine a beacon state and extract messages sent from the transmitter404. Processor 516 may also adjust the DC-to-DC converter 522 forimproved performance.

FIG. 6 is a schematic diagram of a portion of transmit circuitry 600that may be used in the transmit circuitry 406 of FIG. 4. The transmitcircuitry 600 may include a driver circuit 624 as described above inFIG. 4. As described above, the driver circuit 624 may be a switchingamplifier that may be configured to receive a square wave and output asine wave to be provided to the transmit circuit 650. In some cases thedriver circuit 624 may be referred to as an amplifier circuit. Thedriver circuit 624 is shown as a class E amplifier, however, anysuitable driver circuit 624 may be used in accordance with embodimentsof the invention. The driver circuit 624 may be driven by an inputsignal 602 from an oscillator 423 as shown in FIG. 4. The driver circuit624 may also be provided with a drive voltage V_(D) that is configuredto control the maximum power that may be delivered through a transmitcircuit 650. To eliminate or reduce harmonics, the transmit circuitry600 may include a filter circuit 626. The filter circuit 626 may be athree pole (capacitor 634, inductor 632, and capacitor 636) low passfilter circuit 626.

The signal output by the filter circuit 626 may be provided to atransmit circuit 650 comprising a coil 614. The transmit circuit 650 mayinclude a series resonant circuit having a capacitance 620 andinductance (e.g., that may be due to the inductance or capacitance ofthe coil or to an additional capacitor component) that may resonate at afrequency of the filtered signal provided by the driver circuit 624. Theload of the transmit circuit 650 may be represented by the variableresistor 622. The load may be a function of a wireless power receiver508 that is positioned to receive power from the transmit circuit 650.

FIG. 7 is a functional block diagram of a receiver 700 that may be usedin the wireless power transfer system of FIG. 1, in accordance withexemplary embodiments of the invention. The receiver 700 includesreceive circuitry 710 that may include a receive coil 718. The receiver700 may further include switching and signaling circuitry 704 and OverVoltage Protection (OVP)/signaling controller 702. Receiver 700 furthercouples to charging device 750 for providing received power thereto. Insome embodiments, receive coil 718 may be similar to receive coil 518 ofFIG. 5, receive circuitry 710 may be similar to receive circuitry 510 ofFIG. 5, and charging device 750 may be similar to charging device 550 ofFIG. 5. It should be noted that receive circuitry 710 is illustrated asbeing external to charging device 750 but may be integrated intocharging device 750. Energy may be propagated wirelessly to receive coil718 and then coupled through the rest of the switching and signalingcircuitry 704 and the receive circuitry 710 to charging device 750. Byway of example, the charging device 750 may include devices such asmobile phones, portable music players, laptop computers, tabletcomputers, computer peripheral devices, communication devices (e.g.,Bluetooth devices), digital cameras, hearing aids (an other medicaldevices), and the like.

Receive coil 718 may be tuned to resonate at the same frequency, orwithin a specified range of frequencies, as transmit coil 414 (FIG. 4).Receive coil 718 may be similarly dimensioned with transmit coil 414 ormay be differently sized based upon the dimensions of the associatedcharging device 750. By way of example, device 750 may be a portableelectronic device having diametric or length dimension smaller that thediameter of length of transmit coil 414. In such an example, receivecoil 718 may be implemented as a multi-turn coil in order to reduce thecapacitance value of a tuning capacitor (not shown) and increase thereceive coil's impedance. By way of example, receive coil 718 may beplaced around the substantial circumference of charging device 750 inorder to maximize the coil diameter and reduce the number of loop turns(i.e., windings) of the receive coil 718 and the inter-windingcapacitance.

Switching and signaling circuitry 704 may function to protect thereceive circuitry 710 from high voltages induced on receive coil 718 bya transmitter, such as transmitter 204 of FIG. 2. Switching andsignaling circuitry 704 may also function to notify the transmitter ofthe overvoltage condition so that the transmitter can remove theovervoltage condition. As an example, when an overvoltage condition isdetected, switching and signaling circuitry 704 may activate switches toclamp the receiver 700 and change the circuit's impedance to reducecurrent flow. In addition, switching and signaling circuitry 704 maygenerate pulses that are transmitted to the transmitter and/or detunethe receiver 700 (e.g., via linear or digital detuning) to notify thetransmitter that the overvoltage condition has occurred. Switches may beturned on and off according to a pulse width modulation process togenerate the pulses. As described herein, switching and signalingcircuitry 704 may also be referred to as a voltage decay circuit.

OVP/signaling controller 702 may function to measure a voltage receivedby receiver 700 to determine whether the overvoltage condition hasoccurred. OVP/signaling controller 702 may also determine when theovervoltage condition has passed. In some embodiments, OVP/signalingcontroller 702 may also control the switches of switching and signalingcircuitry 704 to generate the appropriate messages to be sent to thetransmitter. OVP/signaling controller 702 and switching and signalingcircuitry 704 are discussed in more detail with respect to FIG. 8A.

FIG. 8A is a schematic diagram of a receiver 800 with a portion ofreceive coil 718 and switching and signaling circuitry 704 that may beused in the receiver 700 of FIG. 7. While receive coil 718 isillustrated as including capacitors 802 and 810, resistors 804 and 808,and inductor 806, this configuration is not meant to be limiting as itshould be apparent to one skilled in the art that receive coil 718 maybe designed in several different ways to achieve the functionality of areceive coil as described above. Likewise, while switching and signalingcircuitry 714 is illustrated as including capacitors 838 and 840,resistors 846 and 848, transistors 842 and 844, and diodes 852 and 854,this configuration is not meant to be limiting as it should be apparentto one skilled in the art that switching and signaling circuitry 704 maybe designed in several different ways to achieve the functionality of aswitching and signaling circuitry as described herein.

In an embodiment, receive coil 718 may receive power wirelessly from atransmitter. During an initial state, OVP/signaling controller 702 mayoutput a low signal such that transistors 842 and/or 844, which act likeswitches, change the impedance of the receiver and/or allow less currentto pass. In other words, transistors 842 and/or 844 may be in an offstate. The current may pass through the rest of switching and signalingcircuitry 704 and reach node 868. OVP/signaling controller 702 may beconfigured to measure a voltage at node 868 and compare this voltage tothreshold voltage values. As an example, OVP/signaling controller 702may include a comparator (not shown) to compare the voltage at node 868with a threshold voltage value. These threshold voltage values may bepredetermined or based on the conditions of receiver 800. One thresholdvoltage value may be an overvoltage threshold value, which is a voltageat which the receiver 800 would be in an overvoltage condition. Forexample, if the voltage at node 868 is equal to or greater than theovervoltage threshold value, then the receiver 800 may be in anovervoltage condition and the transistors 842 and/or 844 may betransitioned to an on state. The overvoltage threshold value may be 26V.

Another threshold value may be a minimum overvoltage threshold value,which is a voltage at which the receiver 800 could open the clamps suchthat transistors 842 and/or 844 are again in an off state. The minimumovervoltage threshold value may be equal to or greater than the voltagenecessary for the receiver 800 to operate in a steady state. In someinstances, it may be desirable to set the minimum overvoltage thresholdvalue to be greater than the voltage necessary for the receiver 800 tooperate in a steady state to account for any delays that may occur whenthe receiver 800 switches the transistors 842 and/or 844 from an onstate to an off state. Note that the receiver 800 may still be in anovervoltage condition even if the minimum overvoltage threshold valuehas been reached. A time that it takes a voltage at node 868 to dropfrom the overvoltage threshold value to the minimum overvoltagethreshold value may not be of a sufficient duration to allow thereceiver 800 to notify the transmitter that it is in an overvoltagecondition. The receiver 800 may remain in an overvoltage condition untilthe transmitter receives notification that the receiver 800 is in anovervoltage condition and reduces and/or removes a power transmitted tothe receiver 800. For example, if the voltage at node 868 is equal orless than the minimum overvoltage threshold value, while the receiver800 may or may no longer be in an overvoltage condition, the receiver800 may open the clamps to allow a voltage at node 868 to increase.Note, however, that if the receiver 800 is already operating in a normalconfiguration (i.e. an overvoltage condition does not currently exist),then the minimum overvoltage threshold value may be ignored for thepurposes of altering a configuration of the receiver 800. The minimumovervoltage threshold value may be 12V.

In an embodiment, if the voltage at node 868 is equal to or exceeds theovervoltage threshold value, then the OVP/signaling controller 702 mayfunction to clamp the receiver 800 by activating the transistors 842and/or 844 such that the transistors 842 and/or 844 change an impedanceof the receiver 800 and/or allow current to pass (i.e. the transistors842 and/or 844 are in an on state). Activating transistors 842 and/or844 may cause the voltage at node 868 to decrease. Once the voltage atnode 868 reaches the minimum overvoltage threshold value, OVP/signalingcontroller 702 may deactivate transistors 842 and/or 844. As describedherein, deactivating transistors 842 and/or 844 may prevent the voltageat node 868 from becoming too low. In some embodiments, the voltage atnode 868 may begin to rise again and the process of activatingtransistors 842 and/or 844 when the voltage reaches the overvoltagethreshold value may be repeated. In this way, the voltage at node 868,an input of receive circuitry 710, may oscillate between acceptablevoltage levels. Receive circuitry 710 may then be able to operatedespite overvoltage conditions.

Note that transistors 842 and/or 844 may serve two or more functions. Inaddition to decaying a received voltage when activated, transistors 842and/or 844 may also be used to generate impedance change signals. In anembodiment, OVP/signaling controller 702 may concurrently activate anddeactivate transistors 842 and/or 844 based on a voltage at node 868 andactivate and deactivate transistors 842 and/or 844 to periodicallygenerate pulses for transmission to a transmitter. The transistors 842and/or 844 may be activated and deactivated according to a pulse widthmodulation process. The pulses may indicate to the transmitter whetherthe receiver is or is not in an overvoltage condition. Based on thisinformation, the transmitter may act accordingly. For example, thetransmitter may reduce a power level of the power transmitter to thereceiver 800. In some embodiments, the transmitter may stop transmittingpower to the receiver 800. Once the transmitter acts to reduce or stoptransmitting power to the receiver 800, then the receiver 800 may nolonger be in an overvoltage condition. In other embodiments, thereceiver 800 may indicate to the transmitter that it is in anovervoltage condition by, for example, sending a signal over anothercommunication channel, such as a 2.4 GHz communication channel (e.g., anout-of-band communication using Bluetooth, RF, etc.). The receiver 800may include an antenna, not shown, separate from the receive coil 718and coupled to the OVP/signaling controller 702, and the signal sentover another communication channel may be transmitted using the antennaof the receiver 800. The transmitter may include an antenna, not shown,similar to the antenna of the receiver 800 to receive the out-of-bandcommunication from the receiver 800. The signal transmitted using theantenna of the receiver 800 to indicate the overvoltage condition may betransmitted concurrently (e.g., simultaneously or nearly simultaneously)with the receiver 800 receiving power from the transmitter via receivecoil 718 and/or with the receiver 800 adjusting the clamps to controlthe voltage at node 868. The signals generated by OVP/signalingcontroller 702 and transistors 842 and/or 844 are described in greaterdetail with respect to FIGS. 9-11.

In alternate embodiments, the OVP/signaling controller 702 may notactivate and deactivate transistors 842 and/or 844 to periodicallygenerate pulses. Instead, it should be noted that the characteristicimpedance of the receiver 800 as seen at the transmitter changes whenthe transistors 842 and/or 844 are activated and deactivated. Thisimpedance change may occur at a frequency determined by a recharge timeof at least one capacitor, such as a rectifying capacitor (not shown).The transmitter may use one or more impedance sensing methods (e.g.,monitoring a current, a voltage and/or a phase signal) to detect thesignal (e.g., the pulse) encoded by the change in the impedance of thereceiver 800. As an example, the monitored signal(s) may be chosen basedon the signal strength.

In addition, a one-shot (not shown) may be coupled between theOVP/signaling controller 702 and the transistors 842 and 844. Theone-shot may function to keep the transistors 842 and/or 844 active evenwhen the OVP/signaling controller 702 has sent a signal to deactivatethe transistors 842 and/or 844. This may allow the voltage at node 868to decay to a safe level, prevent rapid oscillations that could lead toundesirable EMI characteristics, and/or result in a characteristicperiodic change in receiver impedance detectable by the transmitter.When a one-shot is present, the frequency may also be determined basedon a frequency set by the one-shot. Accordingly, the transmitter may besignaled that the receiver 800 is in an overvoltage condition if it seesthe frequency determined by the capacitors and/or the one-shot. In thisway, the transmitter may be signaled as to the overvoltage condition ofthe receiver 800 even without explicit bursts of pulses transmitted tothe transmitter.

FIG. 8B is a schematic diagram of a portion 870 of a transmitter thatmay be used in the transmitter 600 of FIG. 6. The portion 870 mayinclude an envelope detector 871 and/or a pulse detector 875. In anembodiment, the portion 870 may be included in receiver 600. Forexample, the input 873 of the portion 870 may be inserted at node 692,between driver circuit 624 and filter circuit 626 at node 694, betweenfilter circuit 626 and transmit circuit 650 at node 696, or at node 698.The portion 870 may be configured to monitor voltage on thetransmitter's coil to detect load switching, which may identify signalreception. For example, the portion 870 may be configured to detect achange in impedance of a receiver, such as receiver 800 of FIG. 8A.

The envelope detector 871 may include capacitors 872, 876, 882, and/or884, resistors 874, 880, and/or 886, and/or a Schottky diode 878. In anembodiment, the envelope detector 871 may couple to a signal, rectifythe signal, and/or demodulate the signal. While FIG. 8B is illustrateddepicting such components, it should be apparent to one skilled in theart that the envelope detector 871 may be designed in several differentways to achieve the same functionality.

The pulse detector 875 may include one or more band-pass filters 888, arectifier 890, a pulse filter 892, and/or a comparator 894. In anembodiment, the pulse filter 892 may be a low-pass filter.

FIGS. 9-11 are timing diagrams of signals that may be generated by areceiver, such as receiver 800 of FIG. 8A. FIG. 9 illustrates a timingdiagram of the receiver when the receiver is in a normal operatingconfiguration or when the receiver is in an overvoltage condition andthe minimum overvoltage threshold value has been reached. FIG. 9illustrates two waveforms: waveform signals 950 and waveform clamp 980.Waveform signals 950 represents a control signal provided byOVP/signaling controller 702 that determines whether transistors 842and/or 844 of FIG. 8A are activated or deactivated (e.g., if the controlsignal is high, then transistors 842 and/or 844 are activated). Thepulses 902, 904, and 906 of waveform signals 950 represent a pulsing oftransistors 842 and/or 844. FIG. 9 illustrates a condition of thereceiver in which the output of the pulses 902, 904, and 906 is high. Ahigh output of the pulses 902, 904, and 906 may ensure that a processorof the receiver maintains power when in a normal operatingconfiguration.

Waveform clamp 980 represents an intermediate control signal internal toOVP/signaling controller 702 that switches depending on whether theovervoltage threshold value has been reached and whether the minimumovervoltage threshold value has been reached (e.g., if the overvoltagethreshold value has been reached, the intermediate control signal ishigh, and if the minimum overvoltage threshold value has been reached,the intermediate control signal is low). The state of transistors 842and/or 844 may determine the output of the waveform signals 950, and inparticular the output of the pulses 902, 904, and 906. For example, ifthe waveform clamp 980 is low, then the receiver is not in anovervoltage condition or is in an overvoltage condition and the minimumovervoltage threshold value has been reached. Likewise, if the waveformclamp 980 is high, for example, at portion 910, then the receiver is inan overvoltage condition and the minimum overvoltage threshold value hasnot yet been reached. During an overvoltage condition when the minimumovervoltage threshold value has not been reached, the waveform signals950 may be inverted. Thus, when the waveform clamp 980 is low, thewaveform signals 950 may also be low, and when the waveform clamp 980 ishigh, the waveform signals 950 may also be high.

In an embodiment, the pulses 902, 904, and 906 may be of an equal timelength. For example, the pulses 902, 904, and 906 may be 1 μs induration. Likewise, the pulses 902, 904, and 906 may be separated by anequal length of time. For example, a rising edge of pulse 902 to arising edge of pulse 904 may be 6 μs in duration. In total, a durationof the pulses 902, 904, and 906 may be 18 μs. In other embodiments, thepulses 902, 904, and 906 may not be of an equal time length and/or maynot be separated by an equal length of time.

In an embodiment, a standard receiver signaling event may consist of aburst of 4 pulses. For example, the event may consist of 4 167 kHzpulses at a 1/6 duty cycle. The generation of an overvoltage conditionmay require strong transmitter-receiver coupling, which may increase thesignal strength seen at the transmitter. Accordingly, the length of aburst may be reduced to 3 pulses as illustrated in FIG. 9. In someimplementations, as described above, the burst of 3 pulses may stillmaintain a 1/6 duty cycle.

Note that in an embodiment, the pulses 902, 904, and 906 are generatedfor only a portion of waveform signals 950. The portion of waveformsignals 950 after marker 908 may be considered a delay portion of thewaveform, where no pulses are generated and the output is based onwhether the overvoltage threshold value has been reached and whether theminimum overvoltage threshold value has been reached as describedherein. The delay portion of the waveform and the generation of asufficient number of pulses may ensure that an overvoltage conditionevent is distinguished from other changes in impedance. As an example,the waveform signals 950 may repeat itself every 128 μs such that pulsesare generated every 128 μs. In addition, the receiver may be one ofseveral receivers on a given transmitter. For example, 8 receivers maybe powered from one transmitter. If a burst of 3 pulses is sent every128 μs, a maximum number of pulses from 8 receivers may be 240 pulsesevery 260 ms. This may allow the transmitter to distinguish theovervoltage burst from other repetitive changes to the receiver'simpedance.

While FIG. 9 illustrates three pulses 902, 904, and 906, this is notmeant to be limiting and it should be apparent to one skilled in the artthat any number of pulses may be generated to allow for thefunctionality described herein.

FIG. 10 illustrates a timing diagram of the receiver when the receiveris in an overvoltage condition and the minimum overvoltage thresholdvalue has not been reached. FIG. 10 illustrates two waveforms: waveformsignals 1050 and waveform clamp 1080, both of which are similar to theircounterpart in FIG. 9. The pulses 1002, 1004, and 1006, however, areinverted such that an output of the pulse is low. For example, theovervoltage condition event may consist of a burst of 3 pulses 1002,1004, and 1006 at a 5/6 duty cycle. Likewise, the waveform clamp 1080 ishigh to represent the fact the minimum overvoltage threshold value hasnot yet been reached. The transmitter may recognize the low output ofthe pulses 1002, 1004, and 1006 as an indication that the receiver is inan overvoltage condition. For example, the transmitter may detect arising edge or a falling edge to identify the pulses 1002, 1004, and1006. In an embodiment, the transmitter may include an envelope detectorand/or a pulse detector to detect a change in impedance of the receiver,such as the portion 870 illustrated in FIG. 8B. Each time a change inimpedance is detected (e.g., when a pulse is detected), an interrupt maybe generated, and a set number of interrupts may indicate an overvoltagecondition. The transmitter may comprise a counter or other such means tocount the number of times a change in impedance is detected (e.g., tocount the number of received pulses) to identify when an overvoltagecondition has occurred. Note that in embodiments in which a change inimpedance is represented by a pulse, it may not matter whether thepulses are inverted or non-inverted as the transmitter may be able todetect both types of pulses.

Note that inverting the output of the waveform signals 1050, as comparedto the output of the waveform signals 950, may ensure that the voltageat node 868 does not increase substantially during the burst of pulses.Without inverting the output, the voltage at node 868 may increasesubstantially when the receiver attempts to signal to the transmitterthat the receiver is in an overvoltage condition. For example, thevoltage at node 868 may increase because the transistors 842 and/or 844may be deactivated (i.e. open) for a majority of the burst of pulses,counteracting the voltage decay benefits that transistors 842 and/or 844may provide when activated as described herein. Such an increase involtage may prevent the voltage from decaying enough to allow thereceiver to exit the overvoltage condition. In this way, by invertingthe signal, the receiver can signal to a transmitter that it is in anovervoltage condition while also ensuring that the received voltagecontinues to decay to acceptable levels.

FIG. 11 illustrates a timing diagram of the receiver when the receivertransitions from a normal operating state or an overvoltage conditionstate in which the minimum overvoltage threshold value had been reachedto an overvoltage condition state in which the overvoltage thresholdvalue has been reached during a burst of pulses. FIG. 11 illustrates twowaveforms: waveform signals 1150 and waveform clamp 1180, both of whichare similar to their counterpart in FIGS. 9 and 10. Initially, thewaveform clamp 1180 is low indicating that the receiver is in a normaloperating state or that the receiver is in an overvoltage conditionstate and the minimum overvoltage threshold value had been reached. Ifthe signal pulse train coincides with a clamp transition, such as clamptransition 1108, the signaling pulse logic of waveform signals 1150 ischanged at the transition 1108. For example, at transition 1108, thewaveform signals 1150 is inverted such that portion 1106 is no longer apulse and instead an inverted pulse 1110 is generated immediately afterthe transition 1108. The receiver may continue generating an invertedsignal until the receiver is no longer in an overvoltage condition.

FIG. 12A is a partial state diagram of an overvoltage protection schemefor a receiver, such as receiver 800 of FIG. 8A. The partial statediagram of FIG. 12A includes two states. At state 1202, the receiver hasentered an overvoltage condition in which the overvoltage thresholdvalue has been reached, meaning that the voltage at node 868 (V_(reg))is equal to or greater than the overvoltage threshold value (V_(reg)_(_) _(OVP)). In state 1202, the switches, such as transistors 842and/or 844, are turned on or activated. Once V_(reg) reaches the minimumovervoltage threshold value (V_(reg) _(_) _(min) _(_) _(OVP)), thereceiver transitions to state 1204. In state 1204, the switches areturned off or deactivated. Once V_(reg) reaches V_(reg) _(_) _(OVP), thereceiver transitions back to state 1202 and the process repeats.

FIG. 12B is another partial state diagram of an overvoltage protectionscheme for a receiver, such as receiver 800 of FIG. 8A. The partialstate diagram of FIG. 12B includes four states, each of which may beentered into by the receiver concurrently with one of the two states ofFIG. 12A. In other words, the receiver may concurrently be in state 1202or 1204 of FIG. 12A and one of states 1252, 1254, 1256, and 1258 of FIG.12B. In state 1252, the clamp setting is on and the signal out settingis on. In an embodiment, in state 1252, the voltage at node 868 hasequaled or exceeded the overvoltage threshold value. Accordingly, theclamp setting in OVP/signaling controller 702 may be high and thereceiver may also be in state 1202. The signal outputted byOVP/signaling controller 702 may be inverted such that a value of theoutput of the signal is low when the OVP/signaling controller 702attempts to pulse transistors 842 and/or 844. Likewise, in state 1254,the clamp setting is on and the signal setting is off. In an embodiment,in state 1254, the voltage at node 868 has equaled or exceeded theovervoltage threshold value. Accordingly, the clamp setting inOVP/signaling controller 702 may be high and the receiver may also be instate 1202. The signal outputted by OVP/signaling controller 702 may beinverted such that a value of the output of the signal is high when theOVP/signaling controller 702 is not attempting to pulse transistors 842and/or 844. As an example, timing diagram 1260 illustrates a timingdiagram for states 1252 and 1254.

In state 1256, the clamp setting is off and the signal setting is on. Inan embodiment, in state 1256, the voltage at node 868 has reached theminimum overvoltage threshold value. Accordingly, the clamp setting inOVP/signaling controller 702 may be low and the receiver may also be instate 1204. The signal outputted by OVP/signaling controller 702 may benon-inverted such that a value of the output of the signal is high whenthe OVP/signaling controller 702 attempts to pulse transistors 842and/or 844. Likewise, In state 1258, the clamp setting is off and thesignal setting is off. In an embodiment, in state 1258, the voltage atnode 868 has reached the minimum overvoltage threshold value.Accordingly, the clamp setting in OVP/signaling controller 702 may below and the receiver may also be in state 1204. The signal outputted byOVP/signaling controller 702 may be non-inverted such that a value ofthe output of the signal is low when the OVP/signaling controller 702 isnot attempting to pulse transistors 842 and/or 844. As an example,timing diagram 1262 illustrates a timing diagram for states 1256 and1258.

FIG. 13 is a state diagram of a transmitter, such as transmitter 204 ofFIG. 2. Initially, the transmitter transitions to state 1302 and poweris applied. Once power has been applied, the transmitter transitions tobeacon state 1304. At beacon state 1304, the transmitter may monitor forimpedance changes from a receiver. Once the transmitter detectsimpedance changes, the transmitter may transition to receiver probestate 1306. At receiver probe state 1306, the transmitter determineswhether the changes were detected from a valid receiver device. If thetransmitter determines that the device is valid, the transmittertransitions to power transfer state 1308. At power transfer state 1308,the transmitter transfers power to the receiver device. If the receiverdevice receives a voltage that exceeds the overvoltage threshold value,the receiver device may generate signals, a constant signaling tone, orsome other notification to indicate that it has entered an overvoltagecondition, as described herein. If the transmitter detects signals, theconstant signaling, or some other notification indicating an overvoltagecondition has occurred, the transmitter may transition to a reset state1312. During the transition and/or at the reset state 1312, thetransmitter may remove the condition that caused the overvoltagecondition. For example, the transmitter may stop transferring powerwirelessly. At the reset state 1312, the transmitter may wait a periodof time defined by a reset timer. The transmitter may wait a period oftime to allow the receiver device time to exit the overvoltagecondition. Once the reset timer has expired, the transmitter may onceagain transition to a beacon state 1304 and the process is repeated.

FIG. 14 is a state diagram of a receiver, such as receiver 800 of FIG.8A.

Initially, the receiver transitions to a null state 1402. Once a beaconis detected, for example from a transmitter, then the receivertransitions to a registration state 1404. Once a device limits (DL)information frame has expired, the receiver transitions to V_(reg) waitstate 1406. If the voltage at node 868 (V_(reg)) is greater than aminimum voltage necessary for the receiver to operate in a steady state(V_(reg) _(_) _(min)) and less than a maximum voltage necessary for thereceiver to operate in a steady state (V_(reg) _(_) _(max)), then thereceiver may transition to V_(reg) steady state 1410. Otherwise, thereceiver may transition to V_(reg) HIGH/LOW state 1408.

If, while the receiver is in V_(reg) steady state 1410 or V_(reg)HIGH/LOW state 1408, V_(reg) is equal to or exceeds the overvoltagethreshold value (V_(reg) _(_) _(OVP)), then the receiver transitions toV_(reg) OVP state 1414. As described herein, the receiver may transitionback to the V_(reg) steady state 1410 or V_(reg) HIGH/LOW state 1408once V_(reg) has decayed to at least the minimum overvoltage thresholdvalue.

FIG. 15 is a diagram of exemplary receiver control threshold values,such as for receiver 800 of FIG. 8A. As described herein, V_(reg) mayrefer to the voltage at node 868. V_(reg) may initially be set at setthreshold value 1508. As an example, the set threshold value 1508 may be11V. In an embodiment, if V_(reg) equals or exceeds an overvoltagethreshold value 1502, then the receiver may be in an overvoltagecondition. As an example, the overvoltage threshold value 1502 may be26V. If V_(reg) equals or exceeds a maximum voltage threshold value 1504and is less than the overvoltage threshold value 1502, then the receivermay be in a HIGH state. In a HIGH state, the receiver may transmitdevice request (DR) messages and/or information frames. As an example,the maximum voltage threshold value 1504 may be 18V. If V_(reg) equalsor exceeds a minimum voltage threshold value 1510 and is less than themaximum voltage threshold value 1504, then the receiver may be in asteady state, transmitting data send (DS) messages and/or status frames.If V_(reg) is less than the minimum voltage threshold value 1510, thenthe receiver may be in a LOW state, transmitting DR messages and/orinformation frames. As an example, the minimum voltage threshold value1510 may be 8V.

In an embodiment, if the receiver has entered an overvoltage condition,then the receiver may remain in the overvoltage condition state untilV_(reg) decays to the minimum overvoltage threshold value 1506. In someembodiments, the receiver may remain in the overvoltage condition stateeven after V_(reg) decays to the minimum overvoltage threshold value.For example, the receiver may remain in the overvoltage condition stateif the transmitter has not been notified that the receiver is in anovervoltage condition and/or the transmitter has not reduced or removedpower by the time V_(reg) decays to the minimum overvoltage thresholdvalue. As an example, the minimum overvoltage threshold value 1506 maybe 12V. In this way, V_(reg) may oscillate between the overvoltagethreshold value 1502 and the minimum overvoltage threshold value 1506.Note that a V_(reg) scale from 0V to 30V is not meant to be limiting asit should be apparent to one skilled in the art that the techniquesdescribed herein apply to any V_(reg) voltage scale.

FIGS. 16-17 are simulation results of a transmitter and receiver, suchas transmitter 204 of FIG. 2 and receiver 800 of FIG. 8A. FIG. 16 is asimulation result illustrating the oscillation of Vreg during a clamptransition period. The simulation result includes a graph 1602illustrating the oscillation of Vreg, a graph 1604 illustrating a clampwaveform, such as waveform clamp 980, 1080, and/or 1180 describedherein, and a graph 1606 illustrating the signal generated by acontroller, such as OVP/signaling controller 702, to control theswitches, such as transistors 842 and/or 844, as described herein. As anexample, after 1.8 ms, the signaling may start with a 1 μs low pulse.Following the clamp position from high to low, the signaling logic maybe reversed.

FIG. 17 is a simulation result illustrating the oscillation of Vreg andan output of the transmitter signal detection circuit. The simulationresult includes the graph 1602, the graph 1606, and a graph 1702illustrating the output of the transmitter signal detection circuit. Asan example, while the signal detection pulse in graph 1702 may be longerwhen signaling and clamping overlap, both signaling and clamping may bedetected by the transmitter signal detection circuit.

FIG. 18 is a flowchart of an exemplary method 1800 for limiting voltagein a wireless power receiver. Although the method of flowchart 1800 isdescribed herein with reference to the receiver 800 discussed above withrespect to FIG. 8A, a person having ordinary skill in the art willappreciate that the method of flowchart 1800 may be implemented by thereceiver 108 discussed above with respect to FIG. 1, the receiver 208discussed above with respect to FIG. 2, and/or any other suitabledevice. In an embodiment, the steps in flowchart 1800 may be performedby a processor or controller in conjunction with one or more of theOVP/signaling controller 702, the switching and signaling circuitry 704,and the receive coil 718. Although the method of flowchart 1800 isdescribed herein with reference to a particular order, in variousembodiments, blocks herein may be performed in a different order, oromitted, and additional blocks may be added. A person having ordinaryskill in the art will appreciate that the method of flowchart 1800 mayimplemented in any communication device that may be configured toreceive power from a wireless power transmitter and communicate with thewireless power transmitter.

In block 1802, the receiver may receive power wirelessly from atransmitter. In block 1804, the receiver may measure a value of areceived voltage. In an embodiment, the receiver may compare themeasured value to threshold voltage values to determine a state of thereceiver. For example, if the measured voltage exceeds an overvoltagethreshold value, such as overvoltage threshold value 1502 of FIG. 15,then the receiver may be in an overvoltage condition.

In block 1806, the receiver may activate a circuit when the receivedvoltage reaches a first threshold value, the circuit configured toreduce the received voltage. In an embodiment, the circuit may beactivated when the received voltage reaches the overvoltage thresholdvalue. The circuit may include switches that are closed to clamp thereceiver and ground the received current, which results in a decay ofthe received voltage. The switches of the circuit may be controlled by acontroller, such as OVP/signaling controller 702 of FIG. 7.

In block 1808, the receiver may generate a pulse received by thetransmitter when the circuit is activated that signals to thetransmitter that the received voltage reached the first threshold value.In an embodiment, an output of the pulse is inverted if the receivedvoltage reached the first threshold value. The output of the pulse maybe non-inverted if the received voltage reaches a second thresholdvalue.

In block 1810, the receiver may deactivate the circuit when the receivedvoltage reaches a second threshold value. In an embodiment, the secondthreshold value may be the minimum overvoltage threshold value. Theswitches of the voltage decay circuit may be opened to allow thereceived voltage to increase once again.

FIG. 19 is a functional block diagram of a receiver 1900, in accordancewith an exemplary embodiment of the invention. The receiver 1900includes means 1902 for receiving power wirelessly from a transmitter.In an embodiment, means 1902 for receiving power wirelessly from atransmitter may be configured to perform one or more of the functionsdiscussed above with respect to the block 1802. The receiver 1900further includes means 1904 for measuring a value of a received voltage.In an embodiment, means 1904 for measuring a value of a received voltagemay be configured to perform one or more of the functions discussedabove with respect to the block 1804. The receiver 1900 further includesmeans 1906 for activating a circuit when the received voltage reaches afirst threshold value, the circuit configured to reduce the receivedvoltage. In an embodiment, means 1906 for activating a circuit when thereceived voltage reaches a first threshold value, the circuit configuredto reduce the received voltage, may be configured to perform one or moreof the functions discussed above with respect to block 1806. Thereceiver 1900 further includes means 1908 for generating a pulsereceived by the transmitter when the circuit is activated that signalsto the transmitter that the received voltage reached the first thresholdvalue. In an embodiment, means 1908 for generating a pulse received bythe transmitter when the circuit is activated that signals to thetransmitter that the received voltage reached the first threshold valuemay be configured to perform one or more of the functions discussedabove with respect to block 1808. The receiver 1900 further includesmeans 1910 for deactivating the circuit when the received voltagereaches a second threshold value. In an embodiment, means 1910 fordeactivating the circuit when the received voltage reaches a secondthreshold value may be configured to perform one or more of thefunctions discussed above with respect to block 1810.

The various operations of methods described above may be performed byany suitable means capable of performing the operations, such as varioushardware and/or software component(s), circuits, and/or module(s).Generally, any operations illustrated in the Figures may be performed bycorresponding functional means capable of performing the operations.Means for receiving power wirelessly from a transmitter may be providedby a receive coil. Means for measuring a value of a received voltage maybe provided by an OVP/signaling controller. Means for activating avoltage decay circuit when the received voltage reaches a firstthreshold value to reduce the received voltage may be provided by anOVP/signaling controller. Means for generating a pulse may be providedby a circuit, which may include one or more switches. Means fordeactivating the voltage decay circuit when the received voltage reachesa second threshold value may be provided by an OVP/signaling controller.Means for signaling to the transmitter that the received voltage reachedthe first threshold value may be provided by a circuit, which mayinclude one or more switches.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative logical blocks, modules, circuits, andalgorithm steps described in connection with the embodiments disclosedherein may be implemented as electronic hardware, computer software, orcombinations of both. To clearly illustrate this interchangeability ofhardware and software, various illustrative components, blocks, modules,circuits, and steps have been described above generally in terms oftheir functionality. Whether such functionality is implemented ashardware or software depends upon the particular application and designconstraints imposed on the overall system. The described functionalitymay be implemented in varying ways for each particular application, butsuch implementation decisions should not be interpreted as causing adeparture from the scope of the embodiments of the invention.

The various illustrative blocks, modules, and circuits described inconnection with the embodiments disclosed herein may be implemented orperformed with a general purpose processor, a Digital Signal Processor(DSP), an Application Specific Integrated Circuit (ASIC), a FieldProgrammable Gate Array (FPGA) or other programmable logic device,discrete gate or transistor logic, discrete hardware components, or anycombination thereof designed to perform the functions described herein.A general purpose processor may be a microprocessor, but in thealternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices, e.g., a combinationof a DSP and a microprocessor, a plurality of microprocessors, one ormore microprocessors in conjunction with a DSP core, or any other suchconfiguration.

The steps of a method or algorithm and functions described in connectionwith the embodiments disclosed herein may be embodied directly inhardware, in a software module executed by a processor, or in acombination of the two. If implemented in software, the functions may bestored on or transmitted over as one or more instructions or code on atangible, non-transitory computer-readable medium. A software module mayreside in Random Access Memory (RAM), flash memory, Read Only Memory(ROM), Electrically Programmable ROM (EPROM), Electrically ErasableProgrammable ROM (EEPROM), registers, hard disk, a removable disk, a CDROM, or any other form of storage medium known in the art. A storagemedium is coupled to the processor such that the processor can readinformation from, and write information to, the storage medium. In thealternative, the storage medium may be integral to the processor. Diskand disc, as used herein, includes compact disc (CD), laser disc,optical disc, digital versatile disc (DVD), floppy disk and blu ray discwhere disks usually reproduce data magnetically, while discs reproducedata optically with lasers. Combinations of the above should also beincluded within the scope of computer readable media. The processor andthe storage medium may reside in an ASIC. The ASIC may reside in a userterminal. In the alternative, the processor and the storage medium mayreside as discrete components in a user terminal.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

Various modifications of the above described embodiments will be readilyapparent, and the generic principles defined herein may be applied toother embodiments without departing from the spirit or scope of theinvention. Thus, the present invention is not intended to be limited tothe embodiments shown herein but is to be accorded the widest scopeconsistent with the principles and novel features disclosed herein.

What is claimed is:
 1. An apparatus to receive power wirelessly from atransmitter, comprising: a power transfer component configured toreceive power wirelessly from the transmitter; a circuit coupled to thepower transfer component, the circuit configured to reduce a receivedvoltage when activated; a controller configured to activate the circuitwhen the received voltage reaches a first threshold value and configuredto deactivate the circuit when the received voltage reaches a secondthreshold value; and an antenna configured to generate a signal to thetransmitter that signals to the transmitter that the received voltagereached the first threshold value.